[And oh yes, you want to click to envirgingoddessenate – it links to a picture of the area around the crater as well.]

Licinia is about 25 km (15 miles) across – too big to fit in Dawn’s field-of-view from that height. But it does show spectacular detail, including what look like landslides into the bowl from the crater rim; you can see them as dark streaks running down the crater wall. Mounds of material at the base of the crater wall indicate bigger landslides, too. Vesta’s gravity is far weaker than Earth’s – it’s about 1/40th what we experience here – but even then, it’s a force that won’t be denied.

While I was inspecting the crater floor, I saw something that made me laugh out loud. The floor is lit by the distant Sun, but a sharp shadow of the crater rim is cast on it as well. The inky black shadow is irregular due to the uneven crater rim. Inset here is a piece of that shadow line. Do you see the dark shadow "face" looking to the left at the top? It jumped right out at me… and then I saw another face just below it, this time bright and looking to the right and slightly up!

Anyway, Dawn’s visit to Vesta has come to an end. It left the asteroid on September 5, and began the long two-and-a-half year voyage to visit Ceres, the largest of the main belt asteroids between Mars and Jupiter. Vesta is a fascinating place, but so is Ceres, and we know very little about it.

The Dawn mission has been orbiting the asteroid Vesta since July 2011. It’s taken thousands of images of the 500 kilometer-wide (300 mile) rock since then, and JPL just released an amazing video which uses real data from Dawn to simulate flying over the asteroid.

Wow. The animation at Marcia Crater (the bottom crater making up the Snowman triple impact) is especially beautiful and realistic!

Dawn is scheduled to leave Vesta in August and then take a long, slow voyage to the even-larger asteroid Ceres, arriving in 2015. So we still have several months of riveting images of Vesta to look forward to.

Last July, the spacecraft Dawn slipped into orbit around Vesta, one of the largest asteroids in the solar system — the first time a probe had ever orbited a main-belt asteroid. From its height of 16,000 km (almost 10,000 miles), it started mapping the 500 km (300 mile) wide rock, returning the first close-up pictures in amazing detail.

Over time, the height of the spacecraft over the surface was lowered, and it has now attained its lowest altitude orbit: a mere 200 km (120 miles) over the asteroid’s cratered, battered terrain. I mean asteroidain. Whatever. Anyway, it’s now sending back higher-resolution images than ever before, including this very cool one:

[Click to asteroidenate.]

This shows a region of Vesta about 18 km (11 miles) on a side, dominated by a ginormous impact crater. You can see how the crater’s central floor is flat, and you get just a hint of a slightly raised rim around the edge of the crater. The shadow of the rim falling into the crater also suggests variations in the elevation of the rim top (though craters in the floor of the big crater distort the shadow’s edge a little too). I like all the small craters inside the big one; they come in a variety of shapes, some deep, some shallow, and one (near the rim at the bottom of the picture) appears to be sliced in half; I suspect material flowing down the crater wall in a landslide half buried it. Light colored streaks pointing down the crater wall indicate slides do occur. Triggered by other impacts, maybe?

We’ll be seeing lots of amazing images and science coming from this spacecraft over the next few months. Be sure to check the mission’s Image of the Day pages to stay on top of what we’re seeing on Vesta… but be quick, because time’s running out. In May, Dawn will leave Vesta and start a new journey for a new target: the largest asteroid in the solar system, Ceres. It arrives there in 2015.

Very cool. I was struck the most by how the gigantic mound in the center of the south pole basin has actual and substantially-sized craters in it from impacts! Airless bodies have craters all over them — unless they resurface themselves, like Io’s volcanoes do or they have undersurface oceans like Enceladus and Europa — so it’s natural to see craters on a mountain. But usually mountains are relatively small, so big craters would wipe them out. But that mound on Vesta is huge — it rises 23 km (14 miles) above the basin floor! So there’s easily room on it for big craters.

Vesta’s a weird place, and I’m glad we’re studying it so closely. Even more closely than before in fact, since a couple of months ago Dawn dropped to only 750 km from the surface. The images it’s returning now are really amazing… as you can see for yourself!

When we look at the solar system now, we see it after it’s had billions of years of evolution under its belt. Things have changed a lot since it first formed out a swirling disk of material, 4.5 billion years ago. We can make some pretty good guesses about the way things looked back then, though. We can see other systems forming around other stars, for example, to get an idea of what things look like when they’re young.

But we can also look at our own solar system, look at the planets, the comets, the asteroids, and, like astronomical archaeologists, get a glimpse into our own cosmic past.

We know that asteroids formed along with the rest of the system back then. We also know that there are many kinds of asteroids: rocky, metallic, chondritic, some even have ice on or near their surface. Some formed far out in the solar system, and some formed near in. The thing is, we think the vast majority of the asteroids that formed close to the Sun were absorbed by — and by that, I mean smacked into and became part of — the inner planets, including Earth. Only a handful of those asteroids still remain intact after all this time. But now we think we’ve found one: the main belt, 130 km-long asteroid Lutetia.

Using a fleet of telescopes, astronomers carefully measured the spectrum of Lutetia — including spectra taken by the European Rosetta space probe, which visited Lutetia in July 2010 and returned incredible close-up images (see the gallery below). The spectra were then compared to spectra of meteorites found on Earth — meteorites come from asteroids after a collision blasts material from them, so they represent a collection of different kinds of asteroids that we can test in the lab here on Earth.

They found that the spectrum of Lutetia matches a very specific type of meteorite found on Earth, called enstatite chondrites. These rare rocks have a very unusual composition that indicates they were formed very near the Sun, where the heat from our star strongly affected their formation. They have a clearly different composition than meteorites which formed in asteroids farther out in the solar system, and are an excellent indication that Lutetia formed in the inner solar system, in the same region where the Earth did.

So Lutetia is a local! There aren’t many like it in the asteroid main belt between Mars and Jupiter, and in fact it’s a bit of a mystery how it got there; perhaps a near encounter with Earth or Venus flung it out that way, and then the influence of Jupiter made its orbit circular. And there it sits, a relatively pristine example of what the solar system was like when it was young. Currently, the Dawn space mission is orbiting the large asteroid Vesta, and will make its way to Ceres, the largest asteroid, after that. I have to wonder if NASA is eyeing Lutetia as another possible target. It’s an amazing chance to visit an object that may yield a lot of insight into our own planet when it was but a youth.

After all, you can take the asteroid out of the inner solar system, but you can’t take the inner solar system out of the asteroid.

Enceladus is on the left, Vesta on the right (click those links for higher-res shots). Pretty cool, huh? You can see both have two big overlapping craters of roughly the same size, and a smaller third one roughly aligned on top. The set on Vesta is nicknamed — for obvious reasons — "Snowman".

Craters like this form when the impacting object is not a single body; for example, many asteroids are known to be binaries, with both objects about the same size. Getting hit by that would leave two craters either very close together or overlapping, depending on the sizes, distances, and velocities of the impacting bodies.

It’s a 500 km (300 mile) wide asteroid, the second biggest, so its gravity should be strong enough to crush it into a sphere. But it’s not a ball; it’s lumpy and stretched out and, weirdest of all, has an enormous circular depression at its south pole which flattens that entire hemisphere of the little world.

Here’s a recent image taken by the Dawn spacecraft, looking down on Vesta’s strange southern region:

[Click to envestanate.]

You can tell it’s not round! It’s like looking up at a pancake held over your head. The Sun angle is such that the left hand side of the rock is in darkness, which actually helps with giving the image some relief and perspective.

My first assumption is that something really big hit Vesta a long time ago, carving out that basin. Central peaks are common in events like that, smack dab in the middle of the crater (like the gorgeous mountain in the Moon’s Tycho crater), and we see one here, too — that dark spot in the middle, more obvious in an earlier image from Dawn. It’s huge, many kilometers across, but like the asteroid itself it’s weird: it’s really round and smooth, not jagged and sharp like most central peaks. I was at first surprised to find out some scientists are wondering if the basin was from an impact (the usual suspect) or if it were due to some internal process… but then, looking again at the basin and mound, they’re strange enough that maybe sometimes you need to think a little differently.

In a few months, Dawn will drop in from its current 2700 km orbit down to just a few hundred kilometers. When it does, the sharpness of these images will improve dramatically. I hope we get enough information to solve some of the questions about this rock (some detailed commentary on the geology of Vesta has been posted at the DLR website). We have samples of Vesta thanks to meteorites we think came from collisions to the asteroid, so having images and other data to investigate it up close and tie in what we know from the samples will improve our knowledge of this world immensely.

The Dawn spacecraft entered orbit around the main belt asteroid Vesta just a few weeks ago, and images are coming back in dribs and drabs. NASA just released this fantastic one, taken by Dawn’s wide-angle camera:

[Click to protoplanetate.]

Pretty cool, eh? Vesta is about 500 km (300 miles) across, so you’re seeing about half the rock from top to bottom here. The most obvious thing are the two ginormous craters. Note the scale bar; the bottom crater is about 70 km across, and the top one about 50. The fact that they nearly overlap, and are clearly the two biggest features for a big area around them, makes me think it was a double impact. Many asteroids are binary, so two objects a few kilometers in size and orbiting each other 50 or more kilometers apart would do the trick*. [Update: Emily Lakdawalla agrees.]

The bottom crater is weird; the bottom right edge looks like it’s collapsed a bit, marring the near perfect circle of the rim. That feature itself looks like an arc of a circle; might there have been a third rock that hit? That seems unlikely, and I have a hard time believing even a piece of the rim of a previously existing crater would’ve survived the impact!

Also, look around the two craters. See how far away from them, the surface is saturated with smaller impact craters? Near the big two, though, there are fewer. It’s a sure bet the impacts threw out a lot of debris which blanketed the area. The escape velocity of Vesta is a meager 350 meters/sec (about 750 mph); a lot of the stuff blown out on impact would’ve been moving faster than that! So some would’ve escaped the asteroid entirely, but some would’ve settled down over hundreds of square kilometers of area around the site.

Both crater floors have a filled-in appearance. No doubt a lot of energy of the impact went into melting the surface, which flowed inward. Some of that might be slumped material from the crater edges, too. My knowledge of how craters form is limited, especially on asteroids. But I’d love to see high-resolution images of this! That would answer a lot of these questions straight away.

And of course, we’ll be seeing those soon. Dawn is slowly moving down toward Vesta, gradually lowering its height until it settles into its final orbit. At that point, we’ll be getting really high-res shots, and maybe a few enigmas will be solved… only to be replaced, no doubt, by ten times as many. Fun!

[Edited to add: there is that biggish third crater at the top, of course, but I’m not sure it’s related to the other two. It’s much smaller, for one thing, and there are several other craters that size nearby that appear unrelated. It has a softer rim, implying greater age due to erosion (meteorite impacts), and isn’t aligned with them — though the sharp curvature of the asteroid makes that difficult to verify; in some images they look more colinear (that is, aligned).]

Image credit: Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

* At first the size of the impactors was a guess, but then I poked around and found this crater diameter calculator. I put in values for Vesta, and found that the impactors would’ve been roughly 5 km across. My instincts, sometimes, are good.

NASA’s Dawn mission team just revealed the first full-frame image of the giant main-belt asteroid Vesta, and it’s really, really cool:

Yegads! [Click to asteroidenate.]

Vesta is about 500 km (300 miles) across, but is clearly non-spherical, so take that as an average. That’s roughly the size of Colorado! So it’s a big rock, and we’re now seeing it in exquisite detail. This image was taken on July 24, from a distance of about 5000 km (3000 miles).

Man, there’s nothing like being there.

There’s a lot to see. The surface of Vesta is varied, with craters of various sizes (as expected) and depths. I’m very curious to see that there are some darker spots (like in this image) that look like material dredged up from under the surface from impacts; we see this on the Moon and other bodies as well. Some preliminary mineralogical maps show varied distributions of minerals on the surface as well.

Look at how the surface changes: you can see smoother regions, cratered regions, places that are darker, some where it’s brighter. Clearly Vesta has been battered over time — the entire south pole region is an impact basin, and those parallel grooves are from waves of energy moving through the asteroid during the impact event — and hopefully its history will be unraveled when higher-resolution images come in.

In fact, the scientists at the press conference talked at length about how these first images have raised a lot of questions, and stressed several times how more images will reveal the answers. Dawn will orbit Vesta for a full (Earth) year, so we should get plenty of data that will keep folks busy for a long time.

… and it won’t end there. After Dawn leaves Vesta it’ll head over the Ceres, the largest of the main belt asteroids. I wonder what it’ll find there? But it’s too soon to worry about that! We have a whole new world to explore for now.